Mechanochemical Synthesis of Extended Iptycenes.

Iptycenes are intriguing compounds receiving considerable attention as a result of their rigid noncompliant three-dimensional architecture. The preparation of larger iptycenes is often problematic, as a result of their limited solubility and synthetic procedures involving multiple Diels-Alder reactions under harsh extended reaction conditions. We report a mechanochemical synthesis of structurally well-defined iptycenes through an iterative reaction sequence, wherein Diels-Alder reactions and a subsequent aromatization afford higher order iptycenes. We further report that double Diels-Alder reactions under solvent-free condition provide facile access to highly functionalized iptycenes with molecular weights over 2000 Da. Quartz crystal microbalance measurements reveal that these materials efficiently absorb the aromatic hydrocarbons benzene and toluene.

Systematic evaluation of 2,6-linked pyridine-thiophene oligomers.

An efficient synthesis of alternating 2,6-linked pyridine-thiophene (Py-Th) oligomers allows systematic evaluation of their optical and electrochemical properties. The six- and eight-ring oligomers are revealed to be brightly luminescent, even in the solid state. The oligomers are easily reduced but cannot be electrochemically oxidized. The longer oligomers have reduction potentials similar to those reported for pyridine-thiophene polymers of less defined structure. Protonation of the pyridine or substitution at C4 are shown to further modulate the electronic properties and, in combination with the low-lying absolute LUMO energies, these data suggest that the compounds are potential n-type materials worthy of further study.

Determination of n-octanol/water partition and membrane binding of cationic porphyrins.

Porphyrin and their derivatives are being systematically studied as photosensitizers for photodynamic therapy. The ability to predict their membrane partition properties is of key importance to unveil their in vivo activity and applications. Several n-octanol/water partition coefficients (logP(OW)) of porphyrin derivatives have been reported in the literature but large discrepancies have been observed. Reproducible and reliable logP(OW) data for a series of 20 cationic meso-phenyl(pyridyl)porphyrin derivatives were determined by correlating logP(OW) with the partition coefficients measured in a more adequate n-butanol/water system. Linear correlations as a function of the number of positively charged groups bound to the periphery of the porphyrin rings were found within each series. A significant effect of the stereochemistry and nature of the positively charged substituents was also observed, but diminished steadily converging to a similar value in the mono-substituted derivatives. Binding constants to liposomes were shown to be proportional to logP(OW), except for the cis-isomers of doubly charged porphyrins. The cis-isomer presented smaller logP(OW) and higher membrane affinity. The effect was explained based on the amphiphilic nature of the cis-porphyrin.

Synthesis and evaluation of 2,5-linked alternating pyridine-thiophene oligomers.

The first iterative access to alternating 2,5-linked pyridine-thiophene (Py-Th) oligomers is presented. These oligomers exhibit strong absorption and emission, even in the solid state (picture of the longest oligomer, above). Protonation leads to large red shifts in emission and, unlike most known thiophene-containing oligomers, they are readily reduced but not oxidized. These species represent a promising new class of materials for further study and potential application.